Computation hSeek hdl mode i sets the position of handle hdl depending on mode. If mode is:

* AbsoluteSeek: the position of hdl is
set to i.
* RelativeSeek: the position of hdl is
set to offset i from the current position.
* SeekFromEnd: the position of hdl is set
to offset i from the end of the file.

The offset is given in terms of 8-bit bytes.

Error reporting: the hSeek computation may fail with: isPermissionError if a system resource limit would be exceeded.